The complementary components to active microelectronic conductive circuits are resistors, capacitors, and inductors, known as passive components. These components, both the active circuits and the passives, are supported and interconnected on printed wire boards (PWB) in microelectronic devices.
While the integration of active circuit functions using silicon integrated circuits has been a major success, the integration of passive components is still in the developmental stage. Many of the passive components remain discrete, individual components, and often exceed in number by an order of magnitude the number of active integrated circuits on PWBs. This has increased the complexity of the PWBs and decreased the available surface area for other devices. The only alternative in the past has been to increase the size of the printed wire boards.
More recent advances in circuit board design provide for planar components formed on layers of the printed wire board, or for components buried in recesses in the board, resulting in a higher packaging efficiency. This integration of passive components reduces the number of electrical contacts or transitions between the active and passive components, which provides a consequent improvement in electrical performance and a reduction in mechanical stress at these transition points.
The utilization of integral passive components would be particularly advantageous in thin-film packages, and there is a significant effort within the industry to develop organic materials that will function reliably as passive components in microelectronic devices, particularly for thin-film packages. Moreover, as it is expensive to discard printed wire boards, it would be a manufacturing advantage to have an organic material that can be reworked.
In order to achieve the required mechanical performance and desired reworkability, relatively high molecular weight thermoplastics would be the preferred compositions. These materials, however, have high viscosity or even a solid film form, which are drawbacks to the manufacturing process.
Today, one of the primary thrusts within the semiconductor industry is to develop suitable materials for passive components, and particularly materials that would be reworkable.